"unknown error" with new installation

I am a beginner user of owncloud app. I have been using it for data storage and sharing on about 3 devices for an year. I installed the latest windows desktop owncloud file recently and I can't proceed beyond username and password when trying to install as folder on to the my computer. It is coming up "unknown error" when logged-in online. I did the uninstalling and reinstalling on two of my devices (which were syncing fine until I uninstalled it) and I cant go beyond username/password and internal server error. Please guide me.

There is an issue with the server. You need to ask your administrator to check his server logfiles and sort out this problem. There is nothing you can do and there is nothing wrong with your clients.